This invention relates to liquid recovery apparatus, exposure apparatus, exposure methods, and device manufacturing methods, and particularly to exposure apparatus that fill a space between a projection optical system and a substrate with liquid and expose a pattern onto a substrate via the projection optical system and the liquid, and device manufacturing methods using the exposure apparatus.
Semiconductor devices and liquid crystal display devices are manufactured by a so-called photolithographic method that transfers a pattern formed on a mask onto a photosensitive substrate. An exposure apparatus that is used in this photolithographic method is provided with a mask stage that supports a mask, and a substrate stage that supports a substrate. The exposure apparatus transfers a mask pattern onto a substrate via a projection optical system while synchronously moving the mask stage and the substrate stage. Recently, higher resolution of the projection optical system is demanded to obtain higher integration of a device pattern. The resolution of the projection optical system increases as an exposure wavelength that is used becomes shorter and a numerical aperture of the projection optical system becomes larger. Because of this, the exposure wavelength that is used in exposure apparatus has become shortened over the years, and the numerical aperture of projection optical systems has increased. Furthermore, although an exposure wavelength of 248 nm of a KrF excimer laser is currently the mainstream, an exposure wavelength of 193 nm of an ArF excimer laser also has been put into practice. When performing exposure, a depth of focus (DOF) also becomes important in addition to the resolution. The resolution R and the depth of focus δ can be expressed by the following equations.R=k1·λ/NA  (1)δ=±k2·λ/NA2  (2)
Here, λ is an exposure wavelength, NA is a numerical aperture of the projection optical system, and k1, k2 are process coefficients. According to equations (1) and (2), in order to increase the resolution R, by shortening the exposure wavelength λ and increasing the numerical aperture NA, it is understood that the depth of focus δ becomes narrower.
When the depth of focus δ becomes too narrow, it is difficult to match a substrate surface with an image plane of the projection optical system, and there is a possibility that a focus margin may become insufficient at the time of an exposure operation. Therefore, a liquid immersion method has been proposed, as disclosed in, for example, WO99/49504, as a method that substantially shortens an exposure wavelength and broadens the depth of focus. This liquid immersion method fills the space between a lower surface of the projection optical system and a substrate surface with liquid such as water, an organic solvent, or the like, and improves the resolution by taking advantage of the fact that the wavelength of the exposure light in liquid becomes 1/n (n is normally approximately 1.2-1.6 depending on the index of refraction of the liquid) as compared to the wavelength in air, and increases the depth of focus by approximately n-times.
Meanwhile, the exposure apparatus disclosed in the above-mentioned reference has a structure in which a liquid immersion region is formed on a substrate by supplying and recovering liquid using a liquid supply mechanism and a liquid recovery mechanism. However, when the drive of the liquid recovery mechanism stops due to an abnormality of a power source, such as a power outage, etc., the liquid remaining on the substrate leaks or splashes to an outside of the substrate stage. Therefore, the liquid gets on mechanical parts near the substrate stage, and problems occur such as oxidation, failure, etc.